Transistors are the basic building blocks of conventional semiconductor devices, such as memory devices, central processing units (CPU), logic chips, and the like. A number of transistor types are employed in semiconductor devices including bipolar transistors and field effect transistors (FET). The bipolar transistors comprise an emitter, base, and collector and flow current from the emitter to the collector according to current supplied to the base. The field effect transistors comprise a source, drain, and gate and conduct current from the drain to the source according to a voltage supplied to the gate.
A common field effect transistor employed in semiconductor devices is a metal-oxide-semiconductor field effect transistor (MOSFET). Current is conducted from a source to a drain when a sufficient voltage is applied to a gate, otherwise conduction does not occur. The sufficient voltage is referred to as a threshold voltage.
Another common field effect transistor employed in semiconductor devices is a depletion field effect transistor, such as a JFET. The JFET operates similarly to the MOSFET, but instead turns off conduction of current from a source to a drain when a sufficient voltage, also referred to as a threshold voltage, is applied to a gate. Thus, when less than the threshold voltage is applied to the gate, current is conducted from the source to the drain. As a result, depletion field effect transistors have the ability to conduct current from source to drain without requiring power or a voltage applied to its gate.
The amount of current that can flow from the source to the drain of a given JFET is dependent upon the size of the channel region, which for JFET devices is from the source to the drain and underneath the gate. The size of the channel region includes a length or path length between the source and the drain and a depth of the channel region. Variations in the length and/or depth of the channel result in variations in conduction properties, which is typically undesirable.